Project Summary Gliomas are major primary brain tumors, of which glioblastomas (GBM) are the most common and aggressive forms. The poor outcome of traditional treatment for these tumors demands targeted therapies based on identified mechanisms that drive tumor development. Molecular pathology has classified GBM into subtypes, among which the mesenchymal (MES) group is the most malignant. It is still not clear how GBM MES differentiation is achieved. Recent studies found enrichment of tumor-associated macrophages and microglia (TAMs) in MES GBM, suggesting that TAMs may contribute to MES differentiation and could be exploited as therapeutic targets. Transcriptional coactivator with PDZ-binding motif (TAZ) is one of the three transcriptional regulators in driving the GBM MES gene expression program. Aberrant TAZ activation is associated with MES GBM. The goal of this project is to investigate the role of the TAZ-driven MES transcriptional program during TAMs enrichment in GBM, and identify vulnerabilities of GBM MES progression for therapeutics. The first premise of the project is that we have established two novel TAZ-driven GBM mouse models showing enhanced expression of the MES marker and TAMs infiltration. The second premise is that we have identified the non-POU-domain-containing, octamer-binding protein (NONO) as a novel TAZ-binding protein, which is critical for TAZ-driven gene transcription, TAMs infiltration and GBM progression. The third premise is that NONO expression is markedly increased in GBM compared to lower grade gliomas and is associated with TAZ as well as shorter survival. We hypothesize that aberrant TAZ activation promotes GBM to exploit TAMs for malignant progression, and NONO is important in this process by mediating the TAZ transcriptional activities. We further hypothesize that NONO and TAMs could be targeted for therapeutic purposes. We propose the following three specific aims: 1) to determine the mechanism of TAMs recruitment by TAZ-driven GBM; 2) to demonstrate the mechanism by which NONO regulates the TAZ-driven oncogenic transcriptional program in GBM; 3) to evaluate therapeutic effects of NONO inhibition and TAMs blockade in preclinical TAZ-driven GBM models. We will employ a panel of established human GBM cell lines, newly isolated human GBM cells, and mouse models of GBM. Increasing evidence suggests that TAMs contributes to the pathogenesis and therapeutic resistance of GBM. How TAMs are enriched in MES GBM and whether TAMs blockade could benefit therapies for these tumors is still unknown. By establishing the TAZ-driven GBM models and demonstrating the TAZ-NONO regulatory axis in recruiting TAMs, this proposal will reveal vulnerabilities of TAZ-driven GBM progression. Because NONO appears to be nonessential in normal physiology, the GBM- specific vulnerabilities could be a novel avenue for therapeutics.